Photoacoustic Detection of Atmospheric Peroxy Radicals through Ethane-Based Chemical Amplification

This study introduces an innovative method that extends the use of photoacoustic spectroscopy for measuring atmospheric peroxy radicals by integrating it with ethane-based chemical amplification. In this approach, peroxy radicals are quantitatively converted into NO₂, through chemical reactions with ethane and NO, and the resulting NO₂ is subsequently quantified with high sensitivity by photoacoustic spectroscopy. Humidity-dependent amplification factors (chain length) ranging from 5 to 25 have been determined, enabling accurate quantification of the total ambient peroxy radical concentration. With a signal integration time of 90 s and a relative humidity of ∼10%, a 3σ detection limit of ∼38 pptv for peroxy radicals has been achieved. While the current detection limit is not yet sufficient for ambient measurements, the setup is well-suited for laboratory-based kinetic experiments. Further improvements, such as the use of higher-power light sources and additional microphones, are anticipated to enhance performance to a level suitable for field applications. As these advancements are realized, this compact and robust platform is expected to enable more widespread, reliable monitoring of atmospheric peroxy radicals, thereby supporting new insights into atmospheric oxidation processes, air quality, and climate-related phenomena.